How to declare a const String in stable Rust?

I am trying to declare a const String in stable Rust but it does not let me declare it:

const CONSTANT_VALUE: String = String::from("constant value");

fn main() {
    println!("{}", TARGET_PORT_KEY);     
}

It is saying that:

Calls in constants are limited to tuple structs and tuple variants

I do not want to declare my string as literal and call to_string() on literal all the time.

What is the correct way to declare a constant String value?

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